Journal of Sound and < ibration (1999) 228(2), 397 } 420 Article No. jsvi.1999.2411, available online at http://www.idealibrary.com on FINITE ELEMENT DYNAMIC MODEL UPDATING USING MODAL THERMOELASTIC FIELDS L. HUMBERT, F. THOUVEREZ AND L. JEZEQUEL Ecole Centrale de ¸yon, Mechanical Engineering Department ; MR 5513, 36 avenue Guy de Collongue, ¸yon 69131, France (Received 14 December 1998, and in ,nal form 1 June 1999) In this paper, the use of thermoelastic measurements to improve a "nite element model is investigated. The originality of the procedure lies in the use of this stress sum "eld measurement and in the new solution method of the modelling error location stage. Measurement inaccuracies and expansion errors are taken into account through an inequality constraint. Finally, the correction stage is done owing to a variable metric Gauss}Newton method. This updating process has been applied to modal thermoelastic measurements carried out on a thin plate bending with di!erent kinds of defects  1999 Academic Press 1. INTRODUCTION During the last 20 years, "nite element model updating has focused much research, especially in the aeronautical and automotive industries. Many techniques have been proposed, but they were sometimes limited by the available experimental data. The development of high-performance acquisition systems, allowing an accurate and wide investigation of structure behaviour, revives the interest in this subject. In this paper, the thermoelastic measurement technique that provides the experimental dilatation "eld measurement for structures under harmonic loading [1, 2] will be considered. Despite its high sensitivity to local defects and its achievement of a stress "eld measurement, this technique is not yet widespread. This is mainly due to di$culties in the interpretation of such data. Stress experimental values are rarely used for "nite element model improvement, because of the di$culty to introduce stress data in standard updating schemes. Standard "nite element models are built only with an approximation of the displacement "eld. The stresses are a posteriori computed by a derivation and a smoothing of the displacement "eld [3]. To bypass this di$culty, a mixed "nite element approach, based on simultaneous approximation of displacement and stress "elds [3, 4] has been chosen. This non-standard modelling allows easy handling of the thermoelastic measurement as well as all kinds of stress value in the iterative updating process. Updating schemes can be classi"ed into two categories [5]: direct correction methods and iterative correction methods. In the "rst one, models are only mass and sti!ness matrices, which are adjusted in one step by a mathematical 0022-460X/99/470397#24 $30.00/0  1999 Academic Press